Some questions in the questionnaire must appear only if a prior question was answered in a certain way. This is called a 'question pre-condition'.
A single question asks one question in one screen. However, in some cases you'll need to ask more questions on a specific matter. For example, when you need information about a party to an agreement, you normally need more information than just the 'company's name'. It allows you to create several fields related to the same entity.